Reappraisal of the toxicology of ethylene glycol. 3. Mitochondrial effects

Challenges in the diagnosis of ethylene glycol poisoning

Ethylene glycol poisoning, while uncommon, is clinically significant due to the associated risk of severe morbidity or lethality and it continues to occur in many countries around the world. The clinical presentation of ethylene glycol toxicity, while classically described in three phases, varies widely and when combined with the range of differential diagnoses that must be considered makes diagnosis challenging. Early and accurate detection is important in these patients, however, as there is a need to start antidotal treatment early to prevent serious harm. In this article, we will review the literature and provide guidance regarding the diagnosis of ethylene glycol poisoning. While gas chromatography is the gold standard, the usefulness of this test is hampered by delays in access due to availability. Consequently, there are several surrogate markers that can give an indication of ethylene glycol exposure but these must be interpreted with caution and within the clinical context. An in-depth review of these tests, particularly the detection of a raised osmolar gap or an raised anion gap acidosis, will form the main focus of this article.

Methanol and ethylene glycol intoxication

Accidental or intentional ingestion of substances containing methanol and ethylene glycol can result in death, and some survivors are left with blindness, renal dysfunction, and chronic brain injury. However, even in large ingestions, a favorable outcome is possible if the patient arrives at the hospital early enough and the poisoning is identified and appropriately treated in a timely manner. This review covers the common circumstances of exposure, the involved toxic mechanisms, and the clinical manifestations, laboratory findings, and treatment of methanol and ethylene glycol intoxication.

Are calcium oxalate crystals involved in the mechanism of acute renal failure in ethylene glycol poisoning?

INTRODUCTION

Ethylene glycol (EG) poisoning often results in acute renal failure, particularly if treatment with fomepizole or ethanol is delayed because of late presentation or diagnosis. The mechanism has not been established but is thought to result from the production of a toxic metabolite.

METHODS

A literature review utilizing PubMed identified papers dealing with renal toxicity and EG or oxalate. The list of papers was culled to those relevant to the mechanism and treatment of the renal toxicity associated with either compound. ROLE OF METABOLITES: Although the "aldehyde" metabolites of EG, glycolaldehyde, and glyoxalate, have been suggested as the metabolites responsible, recent studies have shown definitively that the accumulation of calcium oxalate monohydrate (COM) crystals in kidney tissue produces renal tubular necrosis that leads to kidney failure. In vivo studies in EG-dosed rats have correlated the severity of renal damage with the total accumulation of COM crystals in kidney tissue. Studies in cultured kidney cells, including human proximal tubule (HPT) cells, have demonstrated that only COM crystals, not the oxalate ion, glycolaldehyde, or glyoxylate, produce a necrotic cell death at toxicologically relevant concentrations. COM CRYSTAL ACCUMULATION: In EG poisoning, COM crystals accumulate to high concentrations in the kidney through a process involving adherence to tubular cell membranes, followed by internalization of the crystals. MECHANISM OF TOXICITY: COM crystals have been shown to alter membrane structure and function, to increase reactive oxygen species and to produce mitochondrial dysfunction. These processes are likely to be involved in the mechanism of cell death.

CONCLUSIONS

Accumulation of COM crystals in the kidney is responsible for producing the renal toxicity associated with EG poisoning. The development of a pharmacological approach to reduce COM crystal adherence to tubular cells and its cellular interactions would be valuable as this would decrease the renal toxicity not only in late treated cases of EG poisoning, but also in other hyperoxaluric diseases such as primary hyperoxaluria and kidney stone formation.

Glyoxylate induces renal tubular cell injury and microstructural changes in experimental mouse

Crystal formation in mice could not be induced either by the administration of ethylene glycol or by glycolate. To clarify the reasons for the difference among these oxalate precursors in mice, we studied renal tubular epithelial injury by immunohistochemical staining of oxidative stress and observing microstructures. Daily intra-abdominal injection of saline solution [10 ml/(kg day)], ethylene glycol[(48.3 mmol/(kg day)], glycolate [1.31 mmol/(kg day)], and glyoxylate [1.35 mmol/(kg day)] into C57BL/6 male mice (8 weeks) was performed for 7 days. Immunohistochemical staining of superoxide dismutase (SOD) and malondialdehyde (MDA), and transmission electron microscopy (TEM) of renal tubular epithelial cells were performed to observe oxidative stress and morphological changes, respectively. Decreased SOD and increased MDA were shown only in glyoxylate-treated mouse kidneys. The TEM study with glyoxylate-treated mouse kidneys demonstrated that the internal structure of mitochondria in renal tubular cells underwent destruction and vacuolization, and microvilli density decreased. These changes in renal tubular cells were located in the crystal-forming area. However, such changes were not detected in the other groups. Each precursor of oxalate induces different changes in renal epithelial cells regarding oxidative stress and the microstructural changes. It is suggested that calcium oxalate crystal formation requires cell injury and morphological changes of renal epithelial tubular cells induced by glyoxylate administration in the mouse kidney.

Calcium oxalate, and not other metabolites, is responsible for the renal toxicity of ethylene glycol

Ethylene glycol (EG) is nephrotoxic due to its metabolism. Many studies suggest that the toxicity is due to oxalate accumulation, but others have conversely suggested that toxicity results from effects of metabolites such as glycolaldehyde or glyoxylic acid on proximal tubule cells. In vivo studies have indicated that accumulation of calcium oxalate monohydrate (COM) corresponds closely with development of toxicity in renal tissue. The present studies were therefore designed to clarify the roles of various metabolites in the mechanism for EG toxicity in vitro by comparing the relative cytotoxicity of EG metabolites using three measures of cell death, ethidium homodimer uptake, lactate dehydrogenase (LDH) release and the conversion of the tetrazolium salt XTT to a colorimetric dye. Human proximal tubule cells in culture were incubated in physiologic buffers for 6h at 37 degrees C with COM (147-735microg/ml, an oxalate equivalence of 1-5mM), glycolate (5-25mM), glyoxylate (0.2-5mM) and glycolaldehyde (0.2-2mM). To assess the effects of acidity on the cytotoxicity, incubations were carried out at pH 6-7.4. The results show that COM dose-dependently increased LDH release and ethidium homodimer uptake, while the other metabolites did not. Conversely, COM had no effect on the XTT assay, while high concentrations of glycolaldehyde and glyoxylate decreased XTT activity, but the latter only at acidic pH. The correlation between the uptake of ethidium homodimer and the release of LDH suggest that COM is cytotoxic to human kidney cells in culture, while the XTT assay does not validly measure cytotoxicity in this system. These results indicate that COM, and not glyoxylate or glycolaldehyde, is the toxic metabolite responsible for the acute tubular necrosis and renal failure that is observed in EG-poisoned patients.

Ethylene glycol poisoning: case report of a record-high level and a review

Ethylene glycol is commonly found in automobile antifreeze and a variety of other commercial products. Ingestion of ethylene glycol, either accidentally or in a suicide attempt, is characterized by severe acidosis, calcium oxalate crystal formation and deposition, and a wide variety of end organ effects that may be fatal. We present a case of a patient who ingested a massive amount of ethylene glycol in a suicide attempt and yet survived with minimal sequelae. A comprehensive review of the literature on the pathology and pathophysiology of ethylene glycol toxicity on each organ system is provided, along with information on diagnosis and current treatment recommendations.

Glycolaldehyde causes DNA-protein crosslinks: a new aspect of ethylene oxide genotoxicity

After in vitro incubation of human peripheral mononuclear blood cells with glycolaldehyde (a putative metabolite of ethylene oxide) for 2 h at 37 degrees C, a dose-dependent increase in DNA crosslinks was observed in a dose range between 1 and 10 mM using the alkaline filter elution technique. The elution rate of mononuclear blood cells after treatment with ionizing radiation (600 cGy) was reduced more than 5-fold if cells were incubated with 10 mM glycolaldehyde for 2 h. After treatment with proteinase K DNA crosslinks were no longer detected in cells incubated with glycolaldehyde. Therefore the crosslinks produced by glycolaldehyde could clearly be identified as DNA-protein crosslinks. Additionally glycolaldehyde induced DNA single-strand breaks in a dose range between 1 and 10 mM. The elution rate of mononuclear blood cells was increased about 18-fold if cells were incubated with 5 mM glycolaldehyde for 2 h using an elution procedure with proteinase K. In vitro incubation of mononuclear cells with ethylene oxide for 2 h at 37 degrees resulted in a dose-dependent increase in DNA single-strand breaks between 0.5 and 10 mM ethylene oxide. Moreover, a time-dependent increase in DNA single-strand breaks after incubation with 1.5 mM ethylene oxide was observed with an increased number of single-strand breaks already detectable after 15 min and a maximum level which was detected after 2 h of incubation. However, no DNA-DNA or DNA-protein crosslinks could be detected although a wide concentration range and many different incubation times were tested. Therefore DNA crosslinks, for which evidence was found in mononuclear blood cells of humans occupationally exposed to ethylene oxide, are possibly generated by glycolaldehyde, a putative intermediate in the metabolism of ethylene oxide to glycolic acid.

Ethylene Glycol Intoxication

Commonly available as automotive antifreeze, ethylene glycol can cause toxicity and death if ingested. It is metabolized to several aldehyde and acid intermediates that can cause severe metabolic acidosis, central nervous system derangements, cardiorespiratory failure, and acute renal failure. A presumptive diagnosis can often be made by assessment of the anion gap and the osmol gap and the finding of metabolic acidosis. Corroborating findings include oxalate crystalluria and urine that fluoresces on exposure to ultraviolet light. Recognition is important because there are specific treatment methods available. Therapy consists of administering sodium bicarbonate to counter the acidosis, ethanol to slow the generation of toxic metabolites, and vitamin cofactors, which may speed detoxification of these intermediates. Hemodialysis is employed to remove both ethylene glycol and its metabolites, to correct the acidbase disturbances, and as treatment for acute renal failure.

Methanol and ethylene glycol poisonings. Mechanism of toxicity, clinical course, diagnosis and treatment

Methanol and ethylene glycol poisonings share many characteristics both clinically and biochemically. Both alcohols are metabolised via alcohol dehydrogenase to their toxic metabolites. Methanol is slowly metabolised to formaldehyde which is rapidly metabolised to formate, the metabolite mainly responsible for methanol toxicity. Formate metabolism depends upon the folate pool which is small in primates compared with other animals. Therefore, formate accumulates in primates during methanol intoxication and is mainly responsible for the metabolic acidosis in the early stage of intoxication. In late stages lactate may also accumulate, mainly due to formate inhibition of the respiratory chain. This tissue hypoxia caused by formate may explain the ocular as well as the general toxicity. Ethylene glycol is metabolised more rapidly than methanol, via alcohol dehydrogenase to glycolaldehyde which is rapidly metabolised to glycolate, the metabolite mainly responsible for the metabolic acidosis in ethylene glycol poisoning. Glycolate is metabolised by various pathways, including one to oxalate which rapidly precipitates with calcium in various tissues and in the urine. Ethylene glycol toxicity is complex and not fully understood, but is mainly due to the severe metabolic acidosis caused by glycolate and to the calcium oxalate precipitation. The clinical course in both poisonings is initially characterised by the development of metabolic acidosis following a latent period, which is more pronounced in methanol poisoning and is the time taken for both alcohols to be metabolised to their toxic metabolites. In methanol poisoning there are usually visual symptoms progressing to visual impairment, whereas ethylene glycol victims develop renal and cardiopulmonary failure. Prognosis is excellent in both poisonings provided that there is early treatment with alkali to combat acidosis, ethanol as an antimetabolite, and haemodialysis to remove the alcohols and their toxic metabolites. Ethanol is also metabolised by alcohol dehydrogenase, but has a much higher affinity for this enzyme than methanol and ethylene glycol. Presence of ethanol will therefore inhibit formation of toxic metabolites from methanol and ethylene glycol. Due to competition for the enzyme, the therapeutic ethanol concentration depends on the concentration of the other two alcohols, but a therapeutic ethanol concentration around 22 mmol/L (100 mg/dl) is generally recommended. Most patients are, however, admitted at a late stage to hospitals not capable of performing analyses of these alcohols or their specific metabolites on a 24-hour basis.(ABSTRACT TRUNCATED AT 400 WORDS)

Dose-dependent toxicity of ethylene glycol monomethyl ether vapour in the rat

Wistar male rats were exposed by inhalation to 50, 100 or 400 ppm of ethylene glycol monomethyl ether (EGME) for 1 to 2 weeks. The overall hepatic drug oxidation reactions, O-deethylation of 7-ethoxycoumarin and 7-ethoxyresorufin and cytochrome P-450 content were only slightly affected by the EGME exposures. NADPH cytochrome c reductase activity showed a tendency toward a dose-dependent decrease in liver, the activity being 73% and 64% of that in the controls after one and two weeks of exposure, at 400 ppm respectively. UDP glucuronosyl transferase activity exhibited a dose-dependent enhancement in liver microsomes after exposure for two weeks to EGME. The enhancement was 1.3- 1.7- and 3.0 fold with exposure to 50, 100 and 400 ppm of EGME respectively. After exposure for one week the UDPglucuronosyltransferase activity in kidney microsomes was similarly enhanced. A dose-related increase in measurable UDPglucuronosyltransferase activity was also obtained in Triton X-100 treated hepatic microsomes. GSH levels of the liver and kidneys in EGME treated animals showed a tendency towards a dose-dependent increase. The activities of low-Km and high-Km aldehyde dehydrogenases in liver were decreased 6 - 14% of that in the controls with exposure to 400 ppm of EGME when glycolaldehyde was used as a substrate. Serum alanine aminotransferase activity was not influenced by inhalation exposures to EGME.

Ethylene glycol poisoning

Although an uncommon cause of death in Great Britain, ethylene glycol poisoning is potentially serious in that renal and cardiopulmonary failure and central nervous system dysfunction can occur when doses of the order of 100 ml or more are ingested. A case is described in which a child who swallowed approximately 100 ml of ethylene glycol was treated by prolonged peritoneal dialysis. In addition, measures were taken to correct a marked acidosis. Substantial amounts of ethylene glycol were removed by the dialysis fluid and the child made a complete physical and mental recovery.